1. Field of the Invention
The present invention relates to a rotary electric shaver in which an outer cutter is provided in the upper part of a shaver main body and hair entering the hair introduction openings of the outer cutter is cut by a rotating inner cutter while it makes elastic contact with the outer cutter.
2. Description of the Related Art
In rotary electric shavers, outer cutters are generally provided depressible (or are provided so as to sink into an outer cutter frame) so as to enhance a tight contact between the outer cutter and the shaving skin. In other words, an outer cutter frame provided on a shaver main body is formed with an outer cutter mounting hole(s), and the outer cutter(s) is installed therein from below so that the outer cutter(s) is elastically pushed upward.
So as to accomplish the structure above, a compression coil spring is ordinarily used, and it is provided on a drive shaft that rotationally drives the inner cutter. An upward return tendency is imparted by this compression coil spring to urge the drive shaft upward, and the inner cutter is thus caused to elastically contact the outer cutter by the upward restorative force of the drive shaft, so that an upward restorative force is imparted to the outer cutter. Because of this structure, the outer cutter can be pushed down and can also pivot within the range of a gap between the outer cutter mounting hole in the outer cutter frame and the outer circumference of the outer cutter.
In rotary electric shavers in which the outer cutter(s) is made capable of making pivot motion with respect to the outer cutter frame, when the range of outer cutter pivot angle is small, and particularly when the curvature of irregularities in the skin surface is small, a tight contact between the outer cutter and the skin becomes is not obtained. Also, when the skin cannot make tight contact with the entire surface of the outer cutter, the utilization efficiency of the outer cutter is poor, and the feel of shaving deteriorates.
One conceivable way of resolving the above-described problem would be to make the allowable angle of pivot motion of the outer cutter with respect to the outer cutter frame larger. If this is done, however, the circumferential edge of the outer cutter will strike the skin at an acute angle, and the contact pressure of the skin against the circumferential edge of the outer cutter will increases. As a result, the skin will be pushed into the hair introduction openings in the outer cutter during shaving, excessively close shaving, with a burning sensation remaining after the shave, will result, which is a problem.
Japanese Patent Application National Publication (Kohyo) No. 9-503424 discloses a rotary electric shaver in which a skin supporting rim is interposed between an outer cutter and an outer cutter frame, so that the skin supporting rim can pivot with respect to the outer cutter frame. More specifically, the skin supporting rim is provided so as to enclose the outer circumference of the outer cutter, and this skin supporting rim is installed so as to be pivotable together with the outer cutter, thus preventing, by the skin supporting rim, the skin from deeply encroaching into the outer circumferential edge of the outer cutter.
FIGS. 6(A) through 7(B) show the pivoting structure disclosed in Japanese Patent Application National Publication (Kohyo) No. 9-503424. FIG. 6(A) is a cross-section taken along the pivot motion axis y, FIG. 6(B) is a cross-section of the pivot supporting point(s) as seen from the direction of the pivot motion axis y, and FIG. 6(C) illustrates the outer cutter and skin supporting rim when they are both tilted. FIGS. 7(A) and 7(B) are illustrations showing the relationship between the pivoted outer cutter and the shaving skin.
In FIGS. 6(A) through 7(B), the reference numeral 10 designates a cutter head unit which is provided on the upper part of a shaver main body (not shown) so that it either can open and close or can be detachably attached. In the cutter head unit 10, three, for instance, sets of cutter units 12, are incorporated at positions that constitute the apexes of an equilateral triangle as seen from above (see FIG. 1). Each cutter unit 12 is comprised of an outer cutter 18 and an inner cutter (not shown) which elastically contacts the inner surface of the outer cutter 18 and is rotated.
The cutter head unit 10 includes an outer cutter frame 14, which either can open and close or can be detachably attached upward with respect to the shaver main body, and three skin supporting rims 16 (only one skin supporting rim is shown) and three outer cutters 18 (only one outer cutter is shown) that are assembled together in the outer cutter frame 14.
Each of the outer cutters 18 is made of thin metal plate, and it has a substantially disc-like cap shape. More specifically, the circumferential edge of a disc is bent (drawn) into a cylindrical shape; and, at the circumferential edge of the opening thereof, a flange 20 is formed to protrude outward in a ring shape. In the circular portion in the center of the outer cutter 18, a multiplicity of slits 22 are formed in a substantially radial pattern. These slits 22 constitute hair introduction openings.
The skin supporting rim 16 are respectively interposed between the outer cutters 18 and the outer cutter frame 14. More specifically, in each of the skin supporting rims 16, a circular outer cutter mounting hole 24 is formed for mounting therein one outer cutter 18 from below; and, in this outer cutter mounting hole 24, the flange 20 of the outer cutter 18 engages from below. The outer circumference of each skin supporting rim 16 is supported by the outer cutter frame 14, so that the skin supporting rim 16 is pivotable in a rim mounting hole 26 formed in the outer cutter frame 14.
More specifically, on the outer circumferential surface of the skin supporting rim 16, a pair of projections 28 (only one of which is shown) project. These projections 28 are formed so as to be perpendicular to a line that passes through the center of the outer cutter 18 and is vertical with respect to the upper surface of the outer cutter 18, that is, vertical to the rotational axis x (see FIG. 6(A)) of the inner cutter, and so as to lie along a straight (diameter) line y passing near the flange 20 of the outer cutter 18. In other words, the projections 28 extend in diagonally opposite directions, with respect to the outer cutter inside thereof, from the outer circumferential surface of the skin supporting rim 16. Each of the projections 28, as seen from FIGS. 6(B) and 6(C), is semicircular arc shape in cross section with a straight line y as the center of such an arc shape and thus has a curved bottom, and the upper surface of each projection 28 has substantially roof-shaped inclined surfaces so that the two sides are inclined downward with the straight line y as the ridge line (straight line where the two inclined surfaces intersect) thereof.
On the other hand, in the rim mounting hole 26 of the outer cutter frame 14, as best seen from FIG. 6(B), a pair of substantially rectangular concavities 30 are formed (FIG. 6(B) show only one concavity 30), so that the two projections 28 of the skin supporting rim 16 engage these concavities 30 (when the shaver has three cutter units 12, then three pairs of concavities 30 are formed in the outer cutter frame 14 so as to correspond to three skin supporting rim 16). Each concavity 30 is formed such that the interior upper surface contains the straight line y of the projection 28 (or is in contact with the ridge line y of the projection 28), and the interior bottom and side surfaces are in slide contact with the curved bottom surface of the projection 28. As a result, the projections 28 turn or rock inside the concavities 30 about the straight line y, and, as a consequence thereof, the skin supporting rim 16 pivots about its projections 28 (more specifically about the straight line y (the straight line y thus being a pivot axis). In other words, the projections 28 (or the straight line y) constitute the axis of pivot of the skin supporting rim 16.
When the projections 28 rock about the straight line y, the inclined upper surfaces of the projections 28 strike the interior upper surface of the concavity 30, and as a result, the pivot angle range of the skin supporting rim 16 is thus restricted by the interior upper surface of the concavity 30 and the inclined upper surfaces of the projections 28 of the skin supporting rim 16. FIG. 6(c) illustrations a situation that the skin supporting rim 16 pivots about the two opposing projections 28 (only one shown), and the right side inclined upper surfaces (only one shown) of such projections 28 come in contact with the interior upper surface of the concavities 30 (only one shown), and a further tilting motion of the skin supporting rim 16 is thus restricted.
In the conventional shaver shown in FIGS. 6(A) and 6(B), when the outer cutter 18 is pressed against the skin during shaving, the outer cutter 18 and the skin supporting rim 16 pivot as shown in FIG. 7(A), in which the reference numeral 32 designates the surface of the skin. FIG. 7(A) illustrates the situation that the pressing force F1 the outer cutter 18 against of the skin against is small when the outer cutter 18 or shaver is pressed against the skin not too strongly, and in FIG. 7(B) shows the situation that the pressing force F2 of the outer cutter 18 against the skin is large when the outer cutter 18 or shaver is pressed against the skin strongly.
When the pressing force F1 is small (FIG. 7(A)), even if the skin 32 bulges out beyond the edge of the outer cutter 18, on the outside of the outer cutter 18, it will contact the upper edge of the skin supporting rim 16. As a result, the contact pressure of the skin 32 against the edge of the outer cutter 18 will not become excessive, and there will be almost no danger of the skin 32 being overly deeply shaved or of a burning sensation being produced.
When, on the other hand, the pressing force F2 is large, the skin 32, as illustrated in FIG. 7(B), would pass over the upper edge of the skin supporting rim 16 and bulge out above the outer cutter 18. In this situation, the contact pressure of the skin 32 against the edge of the outer cutter 18 becomes excessive, and problems occur in which overly close shaves and/or burning sensations are produced.